The invention relates to a method of operating an internal combustion engine (ICE), typically comprised with a vehicle. The invention also relates to a corresponding ICE and to a thereto related computer program product.
In operating an internal combustion engine (ICE) of a vehicle, a considerable amount of heat is generated, heat that must be efficiently dissipated to prevent damage to the ICE. This is generally accomplished by a coolant-based cooling circuit, in which a pump circulates coolant through tubes in a radiator. Air cools the tubes and hence the coolant, and the coolant is then pumped through various components of the ICE, including the combustion chamber of the ICE, thereby cooling the ICE.
In a cold start phase of the ICE, it is typically desirable to allow the temperature of a combustion chamber of the ICE to rapidly increase to be within an ideal operating temperature range, thereby reducing fuel consumption and gas emission. This is in the cold start phase achieved by suppressing the flow of the coolant by using a temperature controlled valve, such as a thermostat, arranged with the cooling circuit. During the flow suppression, the valve is at least partly arranged in a closed state. Once the temperature of the combustion chamber has increase and reached a predetermined threshold, the valve is arranged in an open state and the coolant is allowed to flow freely through the cooling circuit.
With the advance of new vehicle types and method for controlling a vehicle, there will exist scenarios where the above mentioned type of temperature based control of the ICE cooling is counter-productive. Specifically, there is a desire to adapt such a cooling circuit to allow for further reduction in fuel consumption and to minimize the emission produced by the ICE.
According to an aspect of the invention, the above is at least partly alleviated by a method of operating an internal combustion engine (ICE), the ICE comprising a combustion chamber, a cooling circuit, the cooling circuit including a liquid cooling passage arranged in proximity of the combustion chamber, wherein a coolant is arranged to flow within the cooling circuit, and a first valve arranged with the cooling circuit, the first valve arranged to control the flow of the coolant flowing through the liquid cooling passage, wherein the method comprises the steps of determining an operational state of the ICE, and controlling the first valve based on the operational state of the ICE, wherein the first valve is controlled to be in an at least partly closed state if the ICE is in an inoperative state, thereby reducing the flow of the coolant flowing through the liquid cooling passage.
In accordance to the invention, it will be possible to control a temperature reduction rate of the combustion chamber of ICE, such that the time it takes for walls of the combustion chamber to cool down is increased. In a prior art solution where no flow suppression is present when the ICE is in the inoperative state, the coolant can continue to flow due to the principles of thermosiphon, a physical effect allowing passive heat exchange based on natural convection. In fact, this is valid despite that a coolant pump comprised with the cooling circuit is inactive, as long as the temperature of the combustion chamber is above a predetermined temperature for a thermostat typically comprised with the cooling circuit (i.e. the thermostat is in the open state). According to the thermosiphon principles, convective movement of a liquid starts when liquid in the loop is heated, causing it to expand and become less dense, and thus more buoyant than the cooler liquid in the bottom of the loop. Convection moves the heated liquid upwards in the system as it is simultaneously replaced by cooler liquid returning by gravity. In a typical cooling system, the coolant will be cooled down within a radiator comprised with the cooling system (when exposed to ambient air) and continue to circulate even when the ICE is turned off/in the inoperational state.
The inventive concept will in comparison to prior art solutions allow the temperature of the combustion chamber to be kept higher for a longer time period during inoperation of the ICE by controlling the first valve, thereby allowing the temperature of the combustion chamber to have a temperature being closer to an ideal operational temperature range of the combustion chamber once the ICE again is set to its operational state (as compared to a prior-art implementation). Consequently, the ICE may be more efficiently operated already from the start, hence possibly lowering the energy consumption for the ICE. For example, in an implementation where the ICE is operated in a continuous alternation between its operational and inoperational state, the temperature of the walls of the combustion chamber may be kept “as high as possible” also during the inoperation of the ICE, such that the ICE more quickly again may reach its ideal operational temperature range.
In a possible implementation of the invention, a unit for selective catalytic reduction (SCR) is provided with the ICE for reducing particulate emission, where the SCR need to be kept at a relative high operational temperature for operating adequately. In a corresponding manner as discussed above, the SCR will benefit from an in comparison higher temperature of the combustion chamber once the ICE is again entering the operational state. Thus, the inventive concept allows for the SCR more quickly reaching its operational temperature and hence allows for a further reduction of gas emissions (e.g. NOx).
In addition, as the temperature of the combustion chamber may be kept in comparison high, the inventive concept may remove the necessity of using electrical pre-heating measures for increasing the temperature of the combustion chamber when the ICE is again set in its operational state. It should be understood that other methods may be applied for pre-heating, including for example a fuel based solution as is known in the art.
The first valve may be an electrically controllable valve, possibly comprised with a thermostat provided with the cooling circuit. It may also be possible, and within the scope of the invention, to allow the first valve to be provided as an additional component in addition to an already available prior art thermostat (e.g. as an upgrade procedure). It should be noted that the first valve as an alternative may be similarly controlled in a pneumatic or hydraulic manner.
According to a preferred embodiment, the method further comprises the steps of receiving an indication of an upcoming inoperation of the ICE and controlling the first valve to be in the at least partly closed state a time period prior to the upcoming inoperation of the ICE. For example, the ICE may be arranged to operate a generator provided for charging an energy storage device, such as a battery. In such an implementation a current state of charge, SoC, of the battery as compared to a desired charging level may be used in for making a determination/prediction of when the ICE is expected to shut down, i.e. due to the SoC having reached the desired charging level. In a further example, the operation of the ICE may be “pre-planned”, for example in a hybrid implementation as will be further discussed below
The temperature of the walls of the combustion chamber will increase as a consequence of closing the first valve prior to shutting down the ICE, possibly above the ideal operational temperature range. However, this will also give a higher starting temperature once the ICE is entering its inoperational state. Thereby, when the ICE is again activated some time later, the temperature of the walls of the combustion chamber may be even slightly higher; further reducing the time it takes to again reach the ideal operational temperature range.
In a possible embodiment of the invention, the method may also comprise the steps of determining a temperature of the combustion chamber, and comparing the temperature of the combustion chamber with a predetermined threshold, wherein the first valve is controlled to be in the at least partly closed state if the temperature of the combustion chamber is below the predetermined threshold. Accordingly, in case the temperature is determined to be “too high”, the flow suppression may be slightly postponed until the temperature is below the predetermined threshold. This conditioning of controlling the first valve is advantageous as it reduces the risk of overheating the ICE.
The total duration for controlling the first valve in the at least partly closed state may be dependent on an expected duration for the ICE being in its inoperative state. For example, if the duration for the expected inactivity is longer than a predetermined time period, such that the temperature of the chamber walls at the end of the time period is determined to be close to an ambient temperature, it may instead be advantageous to keep the first valve in the open state also during the inoperative of the ICE. Furthermore, the expected duration for inoperation of the ICE may as an alternative be used in the determination of how early prior to the inoperation of the ICE that the first valve should be at least partly closed.
According to another aspect of the present invention there is provided an ICE, comprising a combustion chamber, a cooling circuit, the cooling circuit including a liquid cooling passage arranged in proximity of the combustion chamber, wherein a coolant is arranged to flow within the cooling circuit, and a first valve arranged with the cooling circuit, the first valve arranged to control the flow of the coolant flowing through the liquid cooling passage, wherein the first valve is adapted to be controllable to an at least partly closed state in dependence of an indication of the ICE being inoperative. This aspect of the invention provides similar advantages as discussed above in relation to the previous aspect of the invention.
In a preferred embodiment of the invention, the ICE is comprised as a component of a power system, the power system for example being a vehicle. The vehicle could for example be a truck or a car. However, the ICE could also be comprised with construction equipment, etc. It should however be understood that the ICE could be provided in a stationary arrangement, such as for example an electrical power station (e.g. Genset). The ICE could for example be a diesel engine or an Otto engine, or a hybrid in between.
The ICE could also be arranged as a component of a hybrid system, such as a hybrid vehicle. It should be noted that a vehicle is not necessary limited to a land based vehicle, rather also marine applications (e.g. a boat) are possible and within the scope of the invention.
When the ICE is comprised with a vehicle, the inventive concept could for example be applicable in situations where a start-stop concept is implemented. In such an implementation, the ICE is typically turned off when the vehicle is stationary (e.g. red light). Consequently, in such a situation the first valve may be controlled to also be in the at least partly closed state, thereby allowing the temperature of the chamber walls to only decrease slightly during the stop period for the vehicle.
In another embodiment, where the ICE is comprised with a hybrid vehicle, an upcoming transition from propelling the vehicle using the ICE to using the electrical motor may form a basis for the indication of the upcoming inoperational state of the ICE. Such a transition may for example depend on the topography for a road where the hybrid vehicle is travelling, e.g. based on a pre-planning for propelling the hybrid vehicle. For example, if the ICE is used to propel the vehicle in an uphill scenario, the first valve could be controlled to be at least partly closed a set time period prior to reaching the top of the hill. As mentioned above, the temperature of the chamber walls will as a consequence increase, possibly above the ideal operational temperature range. The exact time for at least partly closing the first valve prior to reaching the top of the hill may thus be selected such that a difference between the ideal operational temperature range for the ICE and the actual temperature of the chamber walls is minimized once the ICE again is arranged in its operational state.
According to a still further aspect of the present invention there is provided a computer program product comprising a computer readable medium having stored thereon computer program means for operating an ICE, the ICE comprising a combustion chamber, a cooling circuit, the cooling circuit including a liquid cooling passage arranged in proximity of the combustion chamber, wherein a coolant is arranged to flow within the cooling circuit, and a first valve arranged with the cooling circuit, the first valve arranged to control the flow of the coolant flowing through the liquid cooling passage, wherein the computer program product comprises code for determining an operational state of the ICE, and code for controlling the first valve based on the operational state of the ICE, wherein the first valve is controlled to be in an at least partly closed state if the ICE is in an inoperative state, thereby reducing the flow of the coolant flowing through the liquid cooling passage. Also this aspect of the invention provides similar advantages as discussed above in relation to the previous aspects of the invention.
The computer readable medium may be any type of memory device, including one of a removable nonvolatile random access memory, a hard disk drive, a floppy disk, a CD-ROM, a DVD-ROM, a USB memory, an SD memory card, or a similar computer readable medium known in the art.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.